Tropical Storm Andrea
On June 5, Tropical Storm Andrea, the first named storm of the 2013 Atlantic hurricane season, formed in the Gulf of Mexico. Andrea made landfall in Florida on June 7 as a strong tropical storm, and continued up the East Coast while transitioning into a post-tropical storm. Combined with another low pressure that produced rain on June 6 through early June 7, the system produced widespread heavy rain and flooding along the East Coast with widespread 3-5 inch totals across the region.
June 6-8, 2013 Storm Archive
June 3 – Seasonable Week, Then Rain Returns
June 4 – Rain Expected Friday-Saturday
June 5 – Rainy Friday From T.S. Andrea
June 6 – Andrea’s Remnants To Produce Heavy Rain
June 7-8 Storm Updates
Radar Archive – to be added soon
The rain event in the region was a result of two storms, a low pressure in the Ohio Valley region, and Tropical Storm Andrea. Andrea, the first named storm of the 2013 Atlantic hurricane season, formed in the central Gulf of Mexico on June 5 out of a tropical wave that slowly drifted through the region in the previous days. Andrea initially struggled with moderate wind shear and a somewhat disorganized structure, but quickly strengthened early on June 6, reaching its peak strength with sustained winds of 65 mph and a minimum pressure of 992 mb.
Near its peak strength, Andrea made landfall in Florida on the evening of June 6, producing widespread heavy rain and isolated tornadoes in Florida. Afterwards, Andrea weakened with sustained winds of 45 mph and a minimum pressure generally around 996 mb. On June 7, Andrea accelerated to the northeast while tracking along the East Coast, merging with a frontal boundary that has produced rain in the interior Northeast since the evening of June 6, and lost its tropical characteristics during 5 PM that day. After becoming post-tropical, the low pressure continued to race northeast just off the coast, brushing eastern Long Island and making landfall in southeastern Massachusetts before exiting the region on June 8.
Forecasting The Storm
Signs of a tropical disturbance or potential tropical storm in the Gulf of Mexico in the first week of June showed up occasionally on the models since the end of May; most of the model guidance, regardless of whether they developed a tropical storm or not, showed a moist tropical air mass making its way up the East Coast during the June 7-9 time frame, and widespread showers were in the forecast near a week away. With the formation of Invest 91L in the Gulf of Mexico at the beginning of June, the model guidance more consistently showed an tropical system tracking up the East Coast, producing widespread heavy rain along the East Coast.
GFS run from 6/4 morning (6z run), showing modeled cumulative rain totals. Heavy rain from Andrea can be seen offshore, with an axis of less than 1/4 inch over the area. Image from NCEP Model Analysis and Guidance.
The main uncertainty with the forecast was regarding the track of the low pressure and the axis of heavy rainfall. There was overall consistency regarding the initial low pressure in the Ohio Valley producing moderate to heavy rain on Saturday afternoon into Sunday morning, especially focusing over Pennsylvania, New York, and north/western parts of the area, although models differed regarding the handling of Andrea. The ECMWF was consistent with bringing Andrea up the coast with widespread heavy rain over 2-3 inches along the I-95 corridor for several days prior to the storm, aside from one run which it temporarily showed a weaker and further east storm. The GFS, however, was consistently showing a weaker, further east, faster and drier storm, with an axis of heavy rain over 2 inches inland, another similar axis offshore, and a narrow dry slot along the I-95 corridor including the NYC area with less than 1/4 to 1/2 inch, significantly underestimating the rainfall amounts that fell along the corridor. The GFS did not show Andrea tracking close enough to the coast to place the heaviest rain axis over the area until the day before the storm, with its 6/6 6z run, when it showed 2 to 3 inches of rain along I-95.
Storm Impact in the Northeast
Radar image from 11:08 AM, showing the initial round of rain over New England and rain from Andrea spreading into New Jersey.
Rain initially began to fell in the area late in the afternoon hours on Thursday, June 6, from the initial area of low pressure in the Ohio Valley. Widespread rain initially spread into Pennsylvania, New York and the western half of the area through the evening and overnight hours, slowly spreading east through the area overnight. Light to moderate rain fell overnight, with moderate to locally heavy rain on Friday morning especially north/west of NYC. By Friday morning, rain totals ranged from 1/2 to 1 inch in NYC and northern NJ, and 1/4 to 1/2 inch in SE NY. Long Island and CT were drier through Friday morning with lower rain totals, under 1/4 inch.
Radar image from 6:58 PM, showing heavy rain covering most of the area, focusing over Long Island and CT. Andrea’s center can be seen over SE Virginia.
Starting mainly after 11 AM to 1 PM, steady moderate to heavy rain from Andrea spread into the area, while Andrea was still located over North Carolina. By 5 PM, much heavier rainfall rates up to 1-2 inch per hour spread into Long Island and southern CT, where the highest storm totals were ultimately recorded. Rainfall temporarily became lighter north/west of NYC, but with additional heavy rain spreading in after 7 PM.
Between 8-11 PM, the focus of the heavier rain shifted north/west into NYC, northern NJ, SE NY and Connecticut, while Long Island continued to see moderate to heavy rain. The warm front made its closest approach to the area, with reports of thunder observed in some areas. The warm front briefly pushed north through Long Island for a few hours, resulting in a brief spike in temperatures into the upper 60s with a south wind, before returning back to north with temperatures back in the upper 50s to low 60s as the low pressure approached. Lighter rain fell after 11 PM to 12 AM, with rain mostly ending by 4 AM as the remnants of Andrea quickly raced to the northeast.